Protection schemes are generally categorized based on whether a redundant channel or path is always available or only available when a failure occurs. In protection schemes, if information is switched from a working channel to a protection channel or working path to a protection path only when a failure occurs, the schemes are referred to as one for one (1:1) protection schemes. In protection schemes, if a protection path or channel is always available and a destination node has the option of choosing which path or channel to use to communicate the information, the schemes are referred to as one plus one (1+1) protections schemes. In “1:1” schemes, either the working channel is switched to a protection path or the information is switched to a protection channel on the protection path. Furthermore, in conventional “1:1” schemes, path protection can be performed if at least one redundant path is available between the origin and destination nodes, and for a path to be fully protected, there must not be any common links in the redundant paths.
Most path protection schemes are generally analogous to two classes of ring protection schemes. The first class of protection schemes is referred to as Bi-directional Line-Switched Ring (“BLSR”) in SONET, or Multiplex section-Shared Protection Ring (“MS-SPRing”) in synchronous digital hierarchy (SDH). The second class is known as Unidirectional Path-Switched Ring (“UPSR”) in synchronous optical networks (SONET), or Dedicated Protection Ring (“DPRing”) in SDH. BLSR and UPSR schemes can be implemented using two or more fibers interconnecting nodes, which either electrically or optically switch traffic between the working and protection paths established by fiber rings.
In BLSR schemes, working channels for each direction connecting two nodes are transmitted on different rings in the same working path. Protection for the working channels is provided using one or more different rings in a common protection path. In UPSR schemes, different working paths for each direction are provided on the same ring and the protection paths are provided on other rings. The protection path in one direction is common with the working path in the other direction.
In the event of a failure of the working path, a destination node for the traffic will switch to the protection path to receive the traffic. In 1:1 schemes, an origin node for the traffic and/or other nodes between the origin and destination node will also switch the traffic to the protection path to route traffic around the failure.
As the demand for transmission capacity continues to grow, there is an increasing need to efficiently use the available transmission capacity and protect the information being transported through the systems. In addition, the increased amount of traffic being carried on each fiber places increased importance on the ability to effectively protect the information, because each failure results in higher revenue losses for service providers. However, currently deployed protection systems have their disadvantages. For example, the protection schemes described above do not allow for wavelength reuse. Once a wavelength channel (λx) is selected and assigned to a particular client, that wavelength is dedicated solely for that particular client. No other client on the DWDM ring may use that specific wavelength. More particularly, there is no allowance for the sharing of wavelengths among clients.
Accordingly, there is a need for optical transmission systems and protection schemes that provide effective protection with increasing wavelength efficiencies for use in long distance communication systems.